The present invention relates generally to electron beam measuring apparatus and more particularly to an electron beam measuring apparatus fit for use in automatically measuring the dimensions of a microscopic pattern on a semiconductor chip during the process of manufacturing semiconductor devices.
Electron beam measuring apparatus have been used for measuring the width of circuit patterns and the diameters of contact holes during the process of manufacturing semiconductor devices.
When desired circuit patterns are formed by etching conductive films such as metal films, semiconductor films or the like deposited on the surfaces of semiconductor wafers, for example, the photographic exposure technique is utilized for forming a photoresist pattern on the surface of a conductive film beforehand and the conductive film is then etched with the photoresist pattern as a mask.
The width and diameter of the photoresist pattern are measured by an electron beam measuring apparatus after the pattern is formed, so that the pattern having nonstandardized dimensions and diameter is prevented from being passed through the etching process. Those having nonstandardized dimensions and the like are sent back to the preceding process setup after their photoresist patterns are peeled off so as to form respective patterns again.
In operation, about five sheets of wafers in total are first selected from one lot (of e.g., 26 sheets) and measurement is automatically made of pattern width and hole diameter in the principal part of each chip arranged in the corner or central portion of each wafer. If any one of the chips is found out of the standard, all wafers in that lot are sent back to the preceding process step where each one is provided with a photoresist pattern again.
Due to the following reasons, the measured results have been known to admit errors in cases where electron beams are used for automatic measurement:
(1) Image is out of focus; PA1 (2) The bottom edge cannot be identified as the contrast is lowered by the charged surface of a sample especially when the hole diameter is measured; and PA1 (3) Starting or terminating point of measurement is misjudged as a foreign substance may be taken as an edge.
The measured results which are outside the range of tolerance do not always signify that the dimensions of the photoresist pattern and the hole diameters are unusual. However, preference has hereto fore been given to measured results, which is problematical in that even those actually within the range of tolerance are regarded as nonconforming.